Index: /trunk/psModules/src/objects/psVectorBracket.c
===================================================================
--- /trunk/psModules/src/objects/psVectorBracket.c	(revision 8885)
+++ /trunk/psModules/src/objects/psVectorBracket.c	(revision 8885)
@@ -0,0 +1,97 @@
+/** @file  psVectorBracket.c
+ *
+ *  Vector Bracketing tools
+ *
+ *  @author EAM, IfA
+ *
+ *  @version $Revision: 1.1 $ $Name: not supported by cvs2svn $
+ *  @date $Date: 2006-09-22 21:35:10 $
+ *
+ *  Copyright 2006 Institute for Astronomy, University of Hawaii
+ *
+ */
+
+#ifdef HAVE_CONFIG_H
+#include <config.h>
+#endif
+
+#include <pslib.h>
+# include "psVectorBracket.h"
+
+// return the last entry below or first entry above key value
+int psVectorBracket (psVector *index, psF32 key, bool above)
+{
+
+    int N;
+    int Nlo = 0;
+    int Nhi = index->n;
+
+    if (above) {
+        while (Nhi - Nlo > 10) {
+            N = 0.5*(Nlo + Nhi);
+            if (index->data.F32[N] > key) {
+                Nhi = N;
+            } else {
+                Nlo = N - 1;
+            }
+        }
+        // at this point, index[Nhi] > key >= index[Nlo]
+        N = Nlo;
+        while ((index->data.F32[N] <= key) && (N < Nhi)) {
+            N++;
+        }
+        return (N);
+    }
+    while (Nhi - Nlo > 10) {
+        N = 0.5*(Nlo + Nhi);
+        if (index->data.F32[N] < key) {
+            Nlo = N;
+        } else {
+            Nhi = N + 1;
+        }
+    }
+    // at this point, index[Nhi] >= key > index[Nlo]
+    N = Nhi;
+    while ((index->data.F32[N] >= key) && (N > Nlo)) {
+        N--;
+    }
+    return (N);
+}
+
+// search for the bins bounding key in index, interpolate the corresponding values
+psF32 psVectorInterpolate (psVector *index, psVector *value, psF32 key)
+{
+
+    int n0 = 0;
+    int n1 = 0;
+
+    // extrapolate at ends
+    if (key < index->data.F32[0]) {
+        n0 = 0;
+        n1 = 1;
+    }
+
+    // extrapolate at ends
+    if (key > index->data.F32[index->n-1]) {
+        n0 = index->n-2;
+        n1 = index->n-1;
+    }
+
+    if (n1 == 0) {
+        n0 = psVectorBracket (index, key, FALSE);
+        n1 = n0 + 1;
+    }
+
+    if (n0 == index->n-1) {
+        n1 = n0;
+        n0 = n1 - 1;
+    }
+
+    float dy = value->data.F32[n1] - value->data.F32[n0];
+    float dx = index->data.F32[n1] - index->data.F32[n0];
+    float dX = key - index->data.F32[n0];
+    float dY = dX * (dy/dx);
+    float result = value->data.F32[n0] + dY;
+    return result;
+}
+
Index: /trunk/psModules/src/objects/psVectorBracket.h
===================================================================
--- /trunk/psModules/src/objects/psVectorBracket.h	(revision 8885)
+++ /trunk/psModules/src/objects/psVectorBracket.h	(revision 8885)
@@ -0,0 +1,8 @@
+
+# ifndef PS_VECTOR_BRACKET_H
+# define PS_VECTOR_BRACKET_H
+
+int psVectorBracket (psVector *index, psF32 key, bool above);
+psF32 psVectorInterpolate (psVector *index, psVector *value, psF32 key);
+
+# endif /* PS_VECTOR_BRACKET_H */